Modern aerospace vehicles (e.g., airplanes, rotorcraft, unmanned aerial vehicles, airships, rockets, and spacecraft) are designed to utilize a variety of lightweight and strong composite materials. One class of these composite materials is referred to generally as “carbon fiber reinforced plastics” (CFRPs). These materials are being incorporated into frame structures as well as various components. For example, liquid reservoirs such as fuel tanks are being constructed from CFRPs.
Measuring the quantity of fuel in an aerospace vehicle's fuel tank is a continuous and critical function. Traditionally, fuel quantity measurement has been accomplished by one or more probes that must be immersed in the fuel. The probes are typically of the electronic-capacitive type which requires electrical penetrations through the fuel storage tank. Electrical penetrations through a fuel tank as well as routing of wire within a fuel tank are not optimum solutions. Though the intended interrogation signals on the wires to the fuel probes are low in power level, the potential for other higher powered unwanted interference signals both man-made and natural can couple onto fuel tank electrical penetrations creating unwanted or even disastrous results. For example, a lightning strike on or in the near vicinity of the air vehicle can induce strong electrical currents on the wiring that penetrates the fuel tank.
Recently, a new class of wireless sensing systems have been developed that use open-circuit, electrically-conductive spiral trace sensors. Details of these sensors and sensing systems are described in U.S. Pat. No. 8,430,327. Briefly, the described wireless sensing system includes a sensor made from an electrical conductor shaped to for an open-circuit, electrically-conductive spiral trace having inductance and capacitance. In the presence of a time-varying magnetic field, the sensor resonates to generate a harmonic response having a frequency, amplitude and bandwidth. A magnetic field response recorder wirelessly transmits the time-varying magnetic field to the sensor and wirelessly detects the sensor's response. Unfortunately, the above-described wireless sensor and sensing system will not function when used on or near conductive materials (such as components made from CFRPs) since the conductive material shields and absorbs the electromagnetic energy generated by the sensor.